Green machine: Cars could run on sunlight and CO2

Experimental solar-powered reactors have shown they can create the building blocks for synthetic liquid fuels. They've got a way to go, but these projects could take a big chunk out of net carbon dioxide emissions without the need for major changes to either vehicles or refuelling infrastructure.

A team at Sandia National Laboratories in Albuquerque, New Mexico, is developing a technique to create some of the ingredients for synthetic fuels from carbon-containing gases. Their cerium-oxide-based system can convert CO2 into carbon monoxide, and can also turn water into hydrogen

The machine, called the Counter Rotating Ring Receiver Reactor Recuperator (CR5) consists of two chambers separated by rotating rings of cerium oxide. As the rings spin, a large parabolic mirror concentrates solar energy onto one side, heating it to 1500 °C and causing the cerium oxide there to release oxygen gas into one of the chambers, whence it is pumped away.

As the ring rotates further it takes the deoxygenated ring off the heat and allows it to cool before it swings round to the other chamber. CO2 is pumped into the second chamber, causing the cooled cerium to steal back an oxygen molecule, producing carbon monoxide and cerium oxide.

The process also works with water instead of CO2, with the reaction this time producing hydrogen.